title: Interaction between meristem tissue layers controls phyllotaxis.
abstract: Phyllotaxis and vein formation are among the most conspicuous patterning processes in plants. The expression and polarization of the auxin efflux carrier PIN1 is the earliest marker for both processes, with mathematical models indicating that PIN1 can respond to auxin gradients and/or auxin flux. Here, we use cell-layer-specific PIN1 knockouts and partial complementation of auxin transport mutants to examine the interaction between phyllotactic patterning, which occurs primarily in the L1 surface layer of the meristem, and midvein specification in the inner tissues. We show that PIN1 expression in the L1 is sufficient for correct organ positioning, as long as the L1-specific influx carriers are present. Thus, differentiation of inner tissues can proceed without PIN1 or any of the known polar transporters. On theoretical grounds, we suggest that canalization of auxin flux between an auxin source and an auxin sink may involve facilitated diffusion rather than polar transport.
authors.affiliation: Institute of Plant Sciences, University of Bern, Bern CH-3013, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kierzkowski
authors.forename: Michael
authors.initials: M
authors.lastname: Lenhard
authors.forename: Richard
authors.initials: R
authors.lastname: Smith
authors.forename: Cris
authors.initials: C
authors.lastname: Kuhlemeier
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001693:Biological Transport, Active; D055459:Facilitated Diffusion; D007210:Indoleacetic Acids / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D018519:Meristem / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D058526:Plant Vascular Bundle / Q000254:growth & development / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; C578308:LAX1 protein, Arabidopsis; C578309:LAX2 protein, Arabidopsis; D026901:Membrane Transport Proteins; C116363:PIN1 protein, Arabidopsis